Although powder coatings have many benefits, it is difficult to coat temperature-sensitive substrates such as plastic, wood, wood composites, and thin cross sections of metal substrates, because normally employed curing temperatures result in damage to such substrates. Thus, the field of powder coating has been active in the development of low curing temperature coating powder to avoid such damage. During the past several years, new technologies have been introduced for providing low temperature cure powder coatings. U.S. Pat. Nos. 5,714,206 and 6,077,610 involve two-component coating powders that can be cured at the low temperatures required for wood and a variety of other metallic and non-metallic substrates. This result is achieved by mixing resin and curing agent components following extrusion in the dry form. The procedure eliminates heating, and thus reaction, of the two components together until they are deposited on the substrate. U.S. Pat. No. 6,703,070 involves a one-component, low curing temperature coating powder. U.S. Pat. No. 5,721,052 discloses epoxy resins cured with imidazole adducts to obtain low temperature cure powder coatings, especially black textured coatings. U.S. Pat. No. 5,824,373 discloses UV curable powder coating to further reduce cure temperatures through the use of UV radiation curing. All of the above patents address the low cure temperature aspect of the powder coatings for heat-sensitive substrates and thus address the problem of substrate degradation at normally used higher powder coating cure temperatures.
The present invention addresses the coating of heat-sensitive substrates, as well as other types of substrates, with use of a novel coating powder comprising SMAI resin, alone or in combination with a second curing agent. Such curing agent(s) result in low curing temperatures, thus facilitating the use of the coating powder for heat-sensitive and other types of substrates. The coating powder of the invention may be produced as a one- or multiple-component powder.